The specific aims of this research project are to test the following hypotheses regarding amphibian regeneration: distal transformation depends upon intercalar regeneration between non-neighboring angular positional values, the would epidermis induces the subjacent layer of blastema cells to assume boundary properties specifying the outline of the regenerate, a gradient of cell surface adhesiveness exists along the proximal-distal axis of the limb. The first two hypotheses will be tested by a variety of transplantation experiments, while the third will be tested by in vitro experiments designed to show differences in the social behavior of blastema cells having different surface properties. The results of these experiments will be used to affirm or deny the concept that the morphogenetic field of the regenerating limb is in the form of a three-dimensional set of boundaries and that positional information in the regenerating limb can be defined in terms of the molecular organization of the cell surface. The significance of this work is that it will provide, on the cell and tissue levels, insight into the organization and nature of morphogenetic fields, and will provide a basis for subsequent molecular analysis. Our long-term goal is to understand the organization and functioning of morphogenetic fields on multiple levels of biological organization within the organism. This goal is important for the potential application of our basic knowledge to the health-related goal of acquiring the ability to regenerate human tissues and organs, or design suitable replacements.